Fix typos and indentation for cluster.py
Fix typos and indentation for cluster.py

This patches fixes a typo and some indentation errors
that were accidentally introduced by premature pushing
of the patch series "Improvements on disk templates, in
particular file storage".

Signed-off-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Jose Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

mbakke/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,grnet/snf-ganeti,leshchevds/ganeti,onponomarev/ganeti,andir/ganeti,bitemyapp/ganeti,leshchevds/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/snf-ganeti,bitemyapp/ganeti,andir/ganeti,mbakke/ganeti,andir/ganeti,ganeti/ganeti,ganeti/ganeti,apyrgio/ganeti,yiannist/ganeti,apyrgio/ganeti,onponomarev/ganeti,dimara/ganeti,grnet/snf-ganeti,ganeti/ganeti,dimara/ganeti,mbakke/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1